It's always dangerous to "assume" anything. Where are the pipes in relationship to the room? A toilet requires a 3" or 4" pipe that is 12" from the center of the drain to the finished wall in the rear and at least 15" from the center of the pipe to each side wall. A shower drain must be 2" diameter and be centered on the shower stall. The shower drain must have a trap already install below the floor. Toilets have their own trap built in and basins are trapped above the floor, usually directly below the basin. Each drain must also be properly vented. It very well may be that these pipes are positioned and vented OK, but you need to be sure. If they are not, then the cost will increase considerably. Cost will also depend on local labor rates and cost of the fixtures you choose. You should have this inspected by a plumber who then can give you some prices.